1. Field of the Invention
The present invention relates to a computation apparatus and method, a quantization apparatus and method, an audio encoding apparatus and method, and a program, and in particular to a computation apparatus and method, a quantization apparatus and method, an audio encoding apparatus and method, and a program that enables a computation process to be performed more efficiently.
2. Description of the Related Art
The MPEG (Moving Picture Expert Group) Audio Standard is known as a scheme for encoding an audio signal. The MPEG Audio Standard includes a plurality of encoding schemes, among which an encoding scheme called “MPEG-2 Audio Standard AAC (Advanced Audio Coding)” is standardized in ISO/IEC (International Organization for Standardization/International Electrotechnical Commission) 13818-7.
Another encoding scheme called “MPEG-4 Audio Standard AAC” is also standardized in the broader ISO/IEC 14496-3. Hereinafter, the MPEG-2 Audio Standard AAC and the MPEG-4 Audio Standard AAC are collectively referred to as an “AAC standard”.
An audio encoding apparatus of the related art that complies with the AAC standard includes a psychoacoustic model holding section, a gain control section, a spectrum processing section, a quantization/encoding section, and a multiplexer section.
The psychoacoustic model holding section divides an audio signal input to the audio encoding apparatus into blocks along the time axis, and analyzes the audio signal for each divided band in accordance with human auditory characteristics to calculate the tolerable error intensity for each divided band.
Meanwhile, the gain control section divides the input audio signal into four equally spaced frequency bands, and performs gain adjustment on the audio signal for a predetermined band.
The spectrum processing section converts the audio signal which has been subjected to the gain adjustment into frequency-domain spectrum data, and performs a predetermined process on the spectrum data on the basis of the tolerable error intensity calculated by the psychoacoustic model holding section. The quantization/encoding section converts the spectrum data (audio signal) which have been subjected to the predetermined process into a code string, on which the multiplexer section multiplexes various information to output a bit stream.
The spectrum processing section discussed above performs a process called “TNS (Temporal Noise Shaping) process” on the frequency-domain spectrum data to control the waveform of quantization noise on the time axis.
For the TNS process, in particular, it has been proposed that the frequency-domain spectrum data be predicted using an FM synthesis scheme capable of expressing a complicated waveform using fewer parameters than those used in linear prediction, a residual signal is obtained as the differential from this signal, and the parameters and the residual signal are encoded, achieving a more efficient encoding process than a process using linear prediction (see Japanese Unexamined Patent Application Publication No. 2006-47561, for example).